The present invention relates generally to high voltage switching circuits, and more specifically to a solid state relay which is capable of switching high power in nanoseconds.
The generation of adequate radio frequency (RF) power is an important function of the transmitter of any radar system. This is because the required transmitter power varies as the fourth root of the range of the radar, if all other factors are constant. To double the range of a radar system, the power has to be increased 16-fold.
Conventional radar systems use one or more traveling wave tube (TWT) amplifiers to output RF signals at commonly used frequency bands at high power. Medium power is, in the present context, defined as electrical power of around 100 watts, and high-power is considered to be electrical power at 1-10kw and above.
While high-voltage power supply units are capable of supplying electrical voltage with the proper magnitudes, this voltage must also be switched on and off, with switching times which may be in microseconds. Mechanical switching devices have inherent limitations in their ability to connect and disconnect the high voltage power supply to the TWT.
Solid state relays appear to be attractive candidates to replace mechanical switches, since they can provide a much faster and smoother connection and disconnect of power than mechanical devices. In the past, however, solid state relays have been limited to the voltage standoff available in a single device. This voltage standoff may be insufficient for the high power needs of a radar transmitter.
The task of providing a solid state relay capable of supplying high power with fast switching speeds is alleviated, to some extent, by the systems described in the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No. 4,367,421, issued to Baker;
U.S. Pat. No. 4,394,590, issued to Honda;
U.S. Pat. No. 4,425,518, issued to Milberger;
U.S. Pat. No. 4,438,356, issued to Fleischer; and
U.S. Pat. No. 4,455,526, issued to Miller.
A solid state relay employing metal oxide semiconductor field effect transistor (MOSFET) power switching transistors is disclosed in Fleischer. The MOSFETs are switched by applying a potential to their gates from an oscillator 10 by way of a control circuit and transformer. A plurality of series connected transistor switches is shown in both Baker and Honda. The Honda patent indicates that the transistors operate simultaneously.
Miller shows a switching regulator having both ON and OFF transformer drives. A very short ON drive pulse charges the capacitance at the gate of the switching transistor and the OFF drive circuit shunts the switching transistor gate-to-source for a short interval to remove the charge. Milberger shows a diode gate circuit for transistors driven through a transformer.
While the prior art is instructive, a need remains for a solid state relay capable of connecting and disconnecting high power at high speeds. The present invention is intended to satisfy that need.